MINERAL PRODUCTS. 1/3 
good workable freestone, but where the dyke passes through it, is so 
much indurated as to be unfit for masonry and is only employed o 
embankments and similar purposes. In Ivildalc, the action o il 
uoon the contiguous shale seems to be plainly discernible part 
it has been qutebleached, perhaps converted into sulphate of alum.ne, 
n 0 “ h er parts it has the aspect of scoria and the iron appears as a 
loose yellow ochre.- At Egton Bridge the blue has shale is changed by 
the dyke to a pale greenish yellow, and made to resemble jasper m 
hardness A white indurated earth in some places separates the dyke 
tan the neighbouring strata; and occasionally the external portions of 
basalt are changed to a friable mass, the iron oxidated, and the felspai 
decomposed to porcelain clay. 
To specify the most valuable mineral productions, to determine their 
relative importance and aptitude for economical uses, and to fix the 
nrinciples which should guide adventurers in quest of them is the 
pi tar duty of a practical geologist. No part of England enjoys 
™ter° advantages from the variety and value of its subterranean 
Treasures than Yorkshire. Its rich mines of iron, lead, and sine, i 
vast Series, and innumerable quarries of building stone, flagstone, 
Tte and lim stone, are productive of increasing wealth and convenience 
at Imme and of considerable benefit to the empire at large. 1 he eastern 
part of the county, though less distinguished m this respect than the 
western, contains many useful minerals, and besides supporting a very 
"ant inland commerce, is capable of furnishing large supplies for 
exportation. 
Coal occurs extensively in the north-eastern part of Yorkshire, in 
the sandstone series between the gray limestone and the dogger, but 
always in thin seams, and generally of inferior quality. Ihe immense 
advantages which would arise to this district from the working of thick 
seams of <mod coal, sufficiently account for the many unsuccessful 
* Rev. L. V. Harcourt, in a valuable communication on the Geology of Cleveland. 
